Field of the Invention
The present invention relates to a heat pump system for a vehicle and a method of controlling the same, and more particularly, to a heat pump system for a vehicle and a method of controlling the heat pump system, which determines that frosting begins on an exterior heat exchanger and carries out a defrosting control if a difference value between outdoor temperature and refrigerant temperature of an outlet side of the exterior heat exchanger is above a frosting decision temperature in a heat pump mode.
Background Art
In general, an air conditioner for a vehicle includes a cooling system for cooling the interior of the vehicle and a heating system for heating the interior of the vehicle. At an evaporator side of a refrigerant cycle, the cooling system converts air into cold air by heat-exchanging the air passing outside an evaporator with refrigerant flowing inside the evaporator so as to cool the interior of the vehicle. At a heater core side of a cooling water cycle, the heating system convers air into warm air by heat-exchanging the air passing outside the heater core with cooling water flowing inside the heater core so as to heat the interior of the vehicle.
In the meantime, differently from the air conditioner for the vehicle, a heat pump system which can selectively carry out cooling and heating by converting a flow direction of refrigerant using one refrigerant cycle has been applied. For instance, the heat pump system includes two heat exchangers: one being an interior heat exchanger mounted inside an air-conditioning case for heat-exchanging with air blown to the interior of the vehicle; and the other one being an exterior heat exchanger for heat-exchanging outside the air-conditioning case, and a direction-adjustable valve for changing a flow direction of refrigerant. Therefore, according to the flow direction of the refrigerant by the direction-adjustable valve, the interior heat exchanger serves as a heat exchanger for cooling when the cooling mode is operated, and serves as a heat exchanger for heating when the heating mode is operated.
Various kinds of the heat pump system for the vehicle have been proposed, and FIG. 1 illustrates a representative example of the heat pump system for the vehicle.
As shown in FIG. 1, the heat pump system for the vehicle includes: a compressor 30 for compressing and discharging refrigerant; a high-pressure side heat exchanger 32 for radiating heat of the refrigerant discharged from the compressor 30; a first expansion valve 34 and a first bypass valve 36 mounted in parallel for selectively passing the refrigerant passing through the high-pressure side heat exchanger 32; an exterior heat exchanger 48 for heat-exchanging the refrigerant passing through the first expansion valve 34 or the first bypass valve 36 outdoors; a low-pressure side heat exchanger 60 for evaporating the refrigerant passing through the exterior heat exchanger 48; an accumulator 62 for dividing the refrigerant passing through the low-pressure side heat exchanger 60 into a gas-phase refrigerant and a liquid-phase refrigerant; an interior heat exchanger 50 for heat-exchanging refrigerant supplied to the low-pressure side heat exchanger 60 with refrigerant returning to the compressor 30; a second expansion valve 56 for selectively expanding the refrigerant supplied to the low-pressure side heat exchanger 60; and a second bypass valve 58 mounted in parallel with the second expansion valve 56 for selectively connecting an outlet side of the exterior heat exchanger 48 and an inlet side of the accumulator 62.
In FIG. 1, the reference numeral 10 designates an air-conditioning case in which the high-pressure side heat exchanger 32 and the low-pressure side heat exchanger 60 are embedded, the reference numeral 12 designates a temperature-adjustable door for controlling a mixed amount of cold air and warm air, and the reference numeral 20 designates a blower mounted at an inlet of the air-conditioning case.
According to the heat pump system having the above structure, when a heat pump mode (heating mode) is operated, the first bypass valve 36 and the second expansion valve 56 are closed, and the first expansion valve 34 and the second bypass valve 58 are opened. Moreover, the temperature-adjustable door 12 is operated as shown in FIG. 1. Accordingly, the refrigerant discharged from the compressor 30 passes through the high-pressure side heat exchanger 32, the first expansion valve 34, the exterior heat exchanger 48, a high pressure side 52 of the interior heat exchanger 50, the second bypass valve 58, the accumulator 62, and a low pressure side 54 of the interior heat exchanger 50 in order, and then, is returned to the compressor 30. That is, the high-pressure side heat exchanger 32 serves as a heater and the exterior heat exchanger 48 serves as an evaporator.
When an air-conditioning mode (cooling mode) is operated, the first bypass valve 36 and the second expansion valve 56 are opened, and the first expansion valve 34 and the second bypass valve 58 are closed. Furthermore, the temperature-adjustable door 12 closes a passage of the high-pressure side heat exchanger 32. Therefore, the refrigerant discharged from the compressor 30 passes through the high-pressure side heat exchanger 32, the first bypass valve 36, the exterior heat exchanger 48, the high pressure side 52 of the interior heat exchanger 50, the second expansion valve 56, the low-pressure side heat exchanger 60, the accumulator 62, and the low pressure side 54 of the interior heat exchanger 50 in order, and then, is returned to the compressor 30. That is, the low-pressure side heat exchanger 360 serves as an evaporator and the high-pressure side heat exchanger 32 closed by the temperature-adjustable door 12 serves as a heater in the same with the heat pump mode.
However, in the heat pump mode (heating mode), the conventional heat pump system for the vehicle carries out heating because the high-pressure side heat exchanger 32 serves as a heater, and the exterior heat exchanger 48 is mounted outside the air-conditioning case 10, namely, at the front side of an engine room of the vehicle, and serves as an evaporator for heat-exchanging with the outdoor air.
In this instance, temperature of the refrigerant introduced into the exterior heat exchanger 48 lowers below the freezing point while the refrigerant heat-exchanges with the outdoor air, so that frosting begins on the surface of the exterior heat exchanger 48.
If frosting on the surface of the exterior heat exchanger 48 is expanded continuously, because the exterior heat exchanger 48 cannot absorb heat, temperature and pressure of the refrigerant inside the system lower, and hence, the heating performance is remarkably reduced since temperature of air discharged to the interior of the vehicle lowers, and stability of the system is also decreased due to introduction of liquid refrigerant into the compressor.